Distributed threshold adjustment for high speed receivers

ABSTRACT

According to one general aspect, a distributed threshold adjuster (DTA) may be interspersed between stages of a multistage amplifier to adjust the DC voltage of an input signal. The DTA may include an input signal terminal configured to receive the input signal. The DTA may also include a plurality of current sources configured to produce an adjustment current signal whose amperage is configured to be increased or decreased by fixed steps in order to adjust the DC voltage of the input signal. The DTA may include a control unit configured to selectively turn on or off the individual current sources of the plurality of current sources to select the amperage of the adjustment current signal. The DTA may further include an output terminal configured to produce an output signal, comprising a combination of the input signal and the adjustment current signal, to a stage of a multistage amplifier.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 12/582,442,filed on Oct. 20, 2009, now issued as U.S. Pat. No. 8,077,060, whichclaims the benefit of U.S. Provisional Application No. 61/172,330, filedon Apr. 24, 2009. Both are entitled “DISTRIBUTED THRESHOLD ADJUSTMENTFOR HIGH SPEED RECEIVERS”. The subject matter of these earlier filedapplications are hereby incorporated by reference.

TECHNICAL FIELD

This description relates to communicating information, and specificallyto the adjustment of a threshold in a receiver.

BACKGROUND

Generally, information is transferred between two or more devices via ananalog signal. Upon receipt this received analog signal is oftenconverted into a digital signal. Frequently, this conversion is aided bya slicer or comparator that decides upon a digital value (e.g., “0”,“1”, etc.) based upon a threshold value.

For example, in one instance, distortion in optical fiber or a wirelesssystem may lead to an asymmetric distribution of ones/highs andzeros/lows around a received logical high and low levels. As a result, areceived eye-opening, as discussed below, may not be centered and thesignal-to-noise ratio at an input sampler or device may be reduced.

SUMMARY

A system and/or method for communicating information, substantially asshown in and/or described in connection with at least one of thefigures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example embodiment of a system relevantto the disclosed subject matter.

FIG. 2 is a block diagram of an example embodiment of a system inaccordance with the disclosed subject matter.

FIG. 3 is a block diagram of an example embodiment of a system inaccordance with the disclosed subject matter.

FIG. 4 is a block diagram of an example embodiment of a system inaccordance with the disclosed subject matter.

FIG. 5 is a block diagram of an example embodiment of a system inaccordance with the disclosed subject matter.

FIG. 6 is a block diagram of an example embodiment of a system inaccordance with the disclosed subject matter.

FIG. 7 is a block diagram of an example embodiment of a system inaccordance with the disclosed subject matter.

FIG. 8 is a flow chart of an example embodiment of a technique inaccordance with the disclosed subject matter.

FIG. 9 is a flow chart of an example embodiment of a technique inaccordance with the disclosed subject matter.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 illustrates an embodiment of a technique to determine a digitalvalue of an analog signal based upon a threshold. In one embodiment, ananalog signal 102 may be received by a device.

The eye diagram 104 is an embodiment of a time domain representation ofa collection of successive traces of the received signal 102 over aperiod lasting 1-bit of information. The magnitude of the signal isrepresented by the Y-axis in volts. In this embodiment the amplitude ofthe signal ranges from a value of “0” (e.g., −5V) to a value of “1”(e.g., +5V); although, it is understood that the above is merely oneillustrative example to which the disclosed subject matter is notlimited. When the signal has a value that is designated a “1” the signaltrace will fall generally within the upper portion of the eye diagram104. Conversely, when the signal has a value that is designated a “0”the signal trace will fall generally within the lower portion of the eyediagram 104.

An eye opening 106 in the eye diagram 104 represents the open portion ofthe eye diagram derived from successive overlapping traces of the signal102 in a 1-bit period as described above. In various embodiments, theeye opening 106 may naturally occur off-center, for example, at +0.36 Vversus 0 V.

In some applications the eye opening 106 may be shifted down from thecenter (along the Y-axis) of the eye diagram 104. For example, in anoptical channel signals are represented as “1”s and “0”s by modulatingthe intensity of a light source from high intensity (e.g., a “1” or +5V)to low intensity (e.g., a “0” or −5V). In practice, however, some levelof signal spread or degradation may be present in the signal forreceived “1”s and “0”s. However, less signal spread or degradation mayoccur for received “0”s. In other words, the signal spread of the “1”smay be larger than the signal spread of the “0”s). As a result, themiddle of the eye from a magnitude standpoint may not be at level 0 Vbut may, instead, be at a lower level, for example, −0.36V.

To compensate for this shifted eye opening, in various embodiments, itis desirable to either adjust a threshold (e.g., adjust the DC level) ofthe signal or adjust a threshold level (e.g., adjust a signal providedto a threshold input) of a circuit (e.g., a slicer) that determineswhether the signal is currently a “0” or a “1”. In the former case, a DCcomponent may be added to the signal to, in effect, raise or lower theeye opening 106 of the signal upwards so that the middle (with respectto the Y-axis) of the eye opening is at a more desirable level. In thelatter case, the level of a threshold input signal for the slicer may besimilarly adjusted.

The eye diagram 108 illustrates that, in one embodiment, the eye opening110 may be significantly below the middle of the eye diagram 108, or, inanother embodiment, above the middle of the eye diagram. For example, inone embodiment, the eye opening 110 may occur between −1.43V and −3.57V,with the eye closing 112 comprising the rest of the eye diagram 108. Itis understood that the eye diagram 108 includes an abstracted version ofa series of superimposed collection of successive traces of a receivedsignal 102 over a period lasting 1-bit of information.

The eye diagram 114 illustrates, in some embodiments, that if thereceived signal (e.g., received signal 102, etc.) is amplified prior toor without regard to an adjustment in the threshold value or DC value ofthe signal, the eye opening 118 may be moved outside the range of thereceiving device. For example, if the received signal comprising the eyediagram 108 is amplified without regard to the “zero point” or center ofthe eye opening 110, the eye closing 112 (which comprises the receivedsignal) may increase to include the entire eye diagram 114 (shown as eyeclosing 116). Said another way, as the received signal is amplified, themid-point of the eye opening 110 (e.g., −2.5V) may be increased oramplified beyond the 5V limitation or rail of the receiving device, andessentially no longer exist.

FIG. 2 is a block diagram of an example embodiment of a system 200 inaccordance with the disclosed subject matter. In one embodiment, thesystem 200 may include an input terminal 204, a distributed thresholdadjuster 206, a multistage amplifier 210 and an analog-to-digitalconverter (ADC) 212. In one embodiment, the system 200 may receive aninput signal 202 and produce an output signal 214. In variousembodiments, the system 200 may also receive one or more enable signals208.

In one embodiment, the system 200 may receive an input signal 202 viainput terminal 204. In various embodiments, this input signal 202 mayinclude an analog signal. In some embodiments, the input signal 202 mayinclude a fiber optic signal. In another embodiment, the input signal202 may include a wireless or wireless-in-origin electrical signal.Although, it is understood that the above are merely a few illustrativeexamples to which the disclosed subject matter is not limited.

In various embodiments, the input signal 202 may then be amplified(e.g., via multistage amplifier 210) and then threshold or DC adjusted(e.g., via distributed threshold adjuster 206). However, as describedabove, this may lead to amplifying the eye opening or threshold levelbeyond the limitations (e.g., electrical rail voltages, etc.) of thereceiving device. Herein, unless expressly stated the term “thresholdadjustment” includes the addition or subtraction of a DC voltage orcurrent level to the input signal.

In one embodiment, threshold adjustment circuits 206 a and 206 b may bedistributed throughout the gain stages 210 a and 210 b such that theinput signal's DC level is adjusted at multiple locations. As will beseen, this structure and/or technique may be applied in variousarchitectures.

In various embodiments, two threshold adjust circuits 206 a and 206 bmay be included in the data path. In the illustrated embodiment, thefirst threshold adjustment circuit 206 a may be at the input (e.g.,after input terminal 204, etc.) while the second threshold adjustmentcircuit 206 b may be after a large gain (e.g., 10 times, etc.) amplifier210 a.

In one embodiment, both threshold adjustment circuits 206 a and 206 bhave, for example, 10 mV resolution and include 6-bits of granularity.In such an embodiment, this configuration may meet both the specifiedrange and resolution criteria for an input signal 202 with apeak-to-peak swing between 10 mV and 1V.

In one embodiment, the system 200 may include a multistage amplifier210. In one embodiment, this multistage amplifier 210 may be configuredto provide a gain of 40. In one embodiment, the first amplifier 210 amay provide a substantially or relatively large amount of gain G1 (e.g.,10 times, etc.). And a second amplifier 210 b may provide a relativelysmall amount of gain G2 (e.g., 4 times, etc.) In the illustratedembodiment, the total gain of the multistage amplifier 210 may be 40;although, it is understood that the above is merely one illustrativeexample to which the disclosed subject matter is not limited.

In such an embodiment, any threshold or DC level adjustment preformed bythe first threshold adjustment circuit 206 a or a similar circuit priorto the amplifier 210 a may produce or yield a coarse or largegranularity of threshold adjustment, as any threshold adjustment will bemultiplied by 10 (in this embodiment) via amplifier 210 a. Likewise, asubsequent threshold adjustment circuit (e.g., threshold adjustmentcircuit 206 b) may provide a fine or smaller granularity of thresholdadjustment.

For example, if the swing of the input signal 202 is relatively small(e.g., between 10 mV and 100 mV), the first or coarse grain thresholdadjustment circuit 206 a may be disabled or shut down (e.g., via enablesignal(s) 208) and only the second or fine grain threshold adjustmentcircuit 206 b may provide the desired DC adjustment signal. Although, itis understood that the above is merely one illustrative example to whichthe disclosed subject matter is not limited. Conversely, if the input ofthe input signal 202 is relatively small (e.g., between 100 mV and 1V),the second or fine grain threshold adjustment circuit 206 b may bedisabled or shut down and the first or coarse grain threshold adjustmentcircuit 206 a may be enabled and thereby adjust the received signal's202 DC level. In such an embodiment, a wide input swing range or voltagerange of the input signal 202 may be handled, allowing for a largerdynamic range of the input signal 202. In another embodiment, both ofthe threshold adjustment circuits 206 a and 206 b may be enabled. It isunderstood that the above are merely a few illustrative examples towhich the disclosed subject matter is not limited.

In one embodiment, the system 200 may include an analog-to-digitalconverter (ADC) 212 configured to convert the amplified analog inputsignal 202 to a digital output signal 214. In one embodiment, the ADC212 may include a slicer or a comparator, for example. In variousembodiments, a final threshold adjustment circuit (not shown) after thefinal amplifier stage (e.g., amplifier 210 b) may be configured toadjust a threshold or DC level (e.g., a second comparator input, etc.)used or employed by the ADC 212 to make a decision in converting theanalog signal to a digital signal, as opposed to directly altering theDC level of the amplified input signal 202.

In one illustrative embodiment, desired input swing range may be between100 mV to 1,000 mV. In such an embodiment, each threshold adjustmentcircuit (e.g., threshold adjuster 206 a and 206 b, etc.) of thedistributed threshold adjuster 206 may include a 6-bit DAC that has theresolution of 10 mV per bit. However, because the second thresholdadjuster 206 b is after the G1 (e.g., 10×, etc.) gain provided byamplifier 210 a, the DC adjustment effectively applied to the inputsignal 202 is only 1 mV (10 mV/10) per bit. Since the first or coarsethreshold adjuster 206 a provides a threshold adjust at the input to themultistage amplifier 210 prior to the gain stages, the thresholdadjustment effectively applied to the input signal 202 remains 10 mV perbit. As a result, in one embodiment, the DC level or threshold of theinput signal 202 may be adjusted over a wide range (e.g., 640 mV=10mV*2^6 bits) with very fine resolution (e.g., 1 mV steps), produced bythe coarse threshold adjuster 206 a and the fine threshold adjuster 206b working in concert. It is understood that the above are merely a fewillustrative examples to which the disclosed subject matter is notlimited.

FIG. 3 is a block diagram of an example embodiment of a system 300 inaccordance with the disclosed subject matter. In one embodiment, thesystem 300 may include an input terminal 204, a distributed thresholdadjuster 206, a multistage amplifier 210 and an analog-to-digitalconverter (ADC) 212. In one embodiment, the system 300 may receive aninput signal 202 and produce an output signal 214.

In one embodiment, the system 300 may include a DC level detectioncircuit 316. In various embodiments, this DC level detection circuit 316may include an eye opening monitor (EOM). In one embodiment, the EOM 316may be configured to measure an average DC voltage level of the analoginput signal 202. In another embodiment, the EOM 316 may be configuredto control the amount of adjustment provided by the distributedthreshold adjuster by, for example, enabling or disabling portions ofthe distributed threshold adjuster 206; although, it is understood thatthe above is merely one illustrative example to which the disclosedsubject matter is not limited.

FIG. 4 is a block diagram of an example embodiment of a system 400 inaccordance with the disclosed subject matter. In one embodiment, thesystem 400 may include an input terminal 204, a distributed thresholdadjuster 206, a multistage amplifier 210 and an analog-to-digitalconverter (ADC) 212. In one embodiment, the system 400 may receive aninput signal 202 and produce an output signal 214.

In one embodiment, the multistage amplifier 210 may be configured toamplify the analog input signal 202 by an amount of gain, for example, again of ‘A’; although, it is understood that the above is merely oneillustrative example to which the disclosed subject matter is notlimited. In the illustrated embodiment, a gain of A is shown, wherein Amay be an arbitrary predefined amount of gain. For example, themultistage amplifier chain could have a gain “A” equal to 40. In anotherembodiment, the amount of gain may be programmable or configurable. Invarious embodiments, the multistage amplifier 210 may consist of a firstportion 410 and a second portion 412.

In one specific illustrative embodiment, the first portion of amplifierstages 410 may include an amplifier 210 a with a gain of 5 and anamplifier 210 b with a gain of 4, for a total amplification of 20. Insuch an embodiment, the second portion of amplifier stage(s) 412 mayinclude an amplifier 210 c which has a gain equal to one-twentieth ofthe total gain A of the multistage amplifier chain.

Likewise, in one embodiment, the distributed threshold adjuster 206 mayinclude three threshold adjusters 206 a, 206 b, and 206 c. Although, a1:1 ratio of amplifier to threshold adjuster has been illustrated, it isunderstood that the above are merely a few illustrative examples towhich the disclosed subject matter is not limited and that any ratio ofamplifiers to threshold adjusters may be used or employed.

In one illustrative embodiment, each of the threshold adjusters 206 a,206 b, and 206 c may include 5-bit DACs. In such an embodiment, thethreshold adjustment of each of the threshold adjusters 206 a, 206 b,and 206 c may be increased to 20 mV per bit. However, it is noted that,in various embodiments, a 5-bit DAC may require or utilize approximatelyhalf the space of a 6-bit DAC, such that three 5-bit DACs may use lessspace (e.g., 25% less) than the previously illustrated two 6-but DACS.In various embodiments, space savings may be further increased byfurther distributing threshold adjusters and reducing the number of bitsper threshold adjuster. In such an embodiment, the threshold adjusters206 a, 206 b, and 206 c may be placed after the input, after the 5×amplifier 210 a, and 4× amplifier 210 b.

In various embodiments, one or more of the threshold adjusters 206 a,206 b, and 206 c may be enabled. For example, in one embodiment, forversions of the input signal 202 having a swing or range of between 200mV and 1V, only the input threshold adjuster 206 a may be enabled orturned on. In such an embodiment, both a predefined range criteria(e.g., greater than 60% of the input range, etc.), where 20 mV*(2^5)=640 mV>60%*1000 mV, and a resolution criteria (e.g., no more than10% of the lower end of the input signal 202 range, etc.), where the 20mV per bit=10% of 200 mV, may be met.

In another embodiment, for versions of the input signal 202 having aswing or range of between 40 mV and 200 mV, only the second thresholdadjuster 206 b may be enabled or turned on. After the 5× gain providedby the first amplifier 210 a, the input signal swing or range may beamplified to a range of between 200 mV and 1V and the situation becomessimilar to the one previously described.

In yet another embodiment, for versions of the input signal 202 having aswing or range of between 10 mV and 50 mV, only the third thresholdadjuster 206 c may be enabled or turned on. After the 20× gain providedby the first portion 410 of the multistage amplifier, the input signalswing or range may be amplified to a range of between 200 mV and 1V andthe situation becomes similar to the one previously described.

It is understood that the above are merely a few illustrative examplesto which the disclosed subject matter is not limited. In variousembodiments, more than one of the threshold adjusters 206 a, 206 b, and206 c may be enabled or turned on, and provide various levels of coarseor fine grain threshold adjustment. In another embodiment, not everystage of the multistage amplifier 210 may have a threshold adjusterpreceding it.

As described above, an apparatus 400 or another embodiment of thedisclosed subject matter may provide relatively constant thresholdadjustment steps which, when referred back to the input, can be calledcoarse or fine. In some embodiments, the effective size of the thresholdadjustment step applied to any intermediate stage of the amplifierchain, may be determined by dividing the step size at the intermediatestage by the gain from the input of the amplifier to that particularpoint in the amplifier chain. Therefore, in various embodiments,threshold adjustment steps applied earlier in the amplifier chain may becoarse while those applied later in the amplifier chain may be fine.

In some embodiments, to achieve a step size that is independent ofvariations arising from temperature, manufacturing etc. one may achievean amplifier gain that is constant. To extend this further, individualgain stages may achieve a relatively constant gain, in such anembodiment. To achieve the same, the circuitry used to determine thethreshold adjustment applied at any intermediate stage may also bedesigned to exhibit small variations. When divided by the (relativelyconstant) gain, the threshold adjustment step size referred to the inputmay be relatively constant within practical limitations, in oneembodiment.

As described below, in various embodiments, an individual gain stage(independent of the threshold adjustment circuit) includesload-resistors which are linked to the stage gain as well as the stepsize and can exhibit fabrication-induced variations. By calibrating theresistor using a known well-controlled resistor, these variations may bereduced. An individual gain stage (independent of the thresholdadjustment circuit) may include a certain amount of current flowingthrough it. By linking this current to a proportional to absolutetemperature (PTAT), gain variations arising from temperature variationsmay be reduced.

In some embodiments, an individual stage's gain can also vary if theoperating point conditions are changed. By applying a thresholdadjustment current such that the output common-mode is relativelyunchanged, the impact of changes in the applied threshold adjustment maybe minimized or reduced.

In such an embodiment, the threshold adjustment applied at anyintermediate stage in the amplifier chain may be linked to a bandgapreferenced biasing circuit so as to minimize variations arising fromtemperature, manufacturing process or supply voltage changes. If theload resistor through which this current flows is uncalibrated, thethreshold adjustment biasing may be provided by a bandgap circuit linkedto an uncalibrated resistor. If the load resistor through which thecurrent flows is calibrated, the threshold adjustment biasing may beprovided by a bandgap circuit linked to a calibrated resistor.

FIG. 5 is a block diagram of an example embodiment of a system 500 inaccordance with the disclosed subject matter. In one embodiment, thesystem 500 provides a more specific illustration of one embodiment ofthe input termination/threshold adjuster pair found in the above figures(e.g., FIG. 2, 3, 4, etc.). For example, in reference to FIG. 2, theinput terminal 204 may include elements 502, 504, 502 n and 504 n; thethreshold adjuster 206 a may include elements 506 and 506 n; and theamplifiers 210 may include the amplifiers 512 and 512 n; although, it isunderstood that the above is merely one illustrative example to whichthe disclosed subject matter is not limited. It is understood that thecircuit of FIG. 5 is merely one illustrative example to which thedisclosed subject matter is not limited.

In one embodiment, the system or circuit 500 may be configured to adjustthe DC level or threshold of a differential input signal (e.g., adifferential version of input signal 202 of FIG. 2) and amplify theinput signal. In one embodiment, the system or circuit 500 may includean input terminal for input signal 502 and 502 n, a control unit 514, acurrent source 506 and 506 n, an output terminal for output signal 510and 510 n, and an amplifier 512 and 512 n.

In one embodiment, the system 500 or input terminal thereof may includea coupling capacitor 504 and/or 504 n configured to pass the AC portionof the input signal 502 to the output terminal of system 500.

Furthermore, the system or circuit 500 may include a pair of resistors508 and 508 n separating the two differential input signal or positiveand negative portions of the input signal. In one embodiment, the pairof resistors or resistive elements 508 may be coupled in series withrespect to one another and in parallel with respect to the outputterminal. In such an embodiment, the resistors or resistive elements 508and 508 n may be configured to produce a common mode voltage (Vcm) 516provided at the common terminal of the resistor elements 508 and 508 n.

In one embodiment, the input terminal may be configured to receive theinput signal 502 (e.g., input signal 202 of FIG. 2). In variousembodiments, the current source 506 may be configured to produce anadjustment current signal whose amperage is configured to be increasedor decreased in order to adjust the DC voltage of the input signal. Insome embodiments, the control unit 514 may be configured to selectivelycontrol the current sources to select the amperage of the adjustmentcurrent signal.

As described below, in various embodiments, the current source 506 mayinclude a plurality of current sources. In such an embodiment, each ofthe plurality of current sources may be configured to provide a currentthat may be selectively added or subtracted from the input signal. Also,in such an embodiment, control unit 514 may be configured to selectivelyturn on or off the individual current sources of the plurality ofcurrent sources to select the amperage of the adjustment current signal.

In various embodiments, the system or circuit 500 may include an outputterminal 510. In some embodiments, the output terminal may be configuredto produce an output signal 510 to a stage of a multistage amplifier512. In such an embodiment, the output signal may include a combinationof the input signal and the adjustment current signal, as describedabove.

FIG. 6 is a block diagram of an example embodiment of a system 600 inaccordance with the disclosed subject matter. FIG. 6 provides additionaldetail regarding a threshold adjuster of a distributed thresholdadjuster system; although, it is understood that the above is merely oneillustrative example to which the disclosed subject matter is notlimited.

In one embodiment, the system or circuit 600 may include a currentsource 506. In various embodiments, the current source 506 may include aplurality of current sources 610 (e.g., current sources 610 a, 610 b,610 x, etc.). In such an embodiment, each of the plurality of currentsources 610 may be configured to provide a current that may beselectively added or subtracted from the input signals 502 and 502 n.

In some embodiments, each current source or current cell 610 may beconfigured to produce a positive and a negative adjustment current. Invarious embodiments, the plurality of current sources 610 may be coupledsuch that the positive current signal is combined with a positivedifferential input signal 502 and the negative current signal iscombined with a negative differential input signal 502 n. In someembodiments, the absolute values of the amperage of the positive andnegative current signals may be substantially equal.

In various embodiments, each current source or current cell 610 mayinclude a current source 616 and a pair of switches 618 and 618 n. Invarious embodiments, these switches 618 may be controlled by a controlunit. In various embodiments, the control unit may include a DAC, asdescribed above. In such an embodiment, each bit of the DAC may beconfigured to control one of the plurality of current sources 610. Insuch an embodiment, as the number of bits of the DAC are “turned on” orenabled, the amount of current provided by the current source 506 may beincreased, or conversely decreased as the bits are “turned off” ordisabled. Although, it is understood that the above is merely oneillustrative example to which the disclosed subject matter is notlimited.

In one embodiment, the plurality of current sources 610 may be coupledbetween the input terminal of the input signal 502 and 502 n and thepair of resistors 508 and 508 n. In some embodiments, the plurality ofcurrent sources 610 may be coupled such that the output 510 and 510 ncommon mode voltage remains substantially constant regardless of theamperage of the adjustment current source 506. By minimizing changes inthe operating points of the devices comprising the amplifier chain, thisenables a reduction in the gain variations per stage of the amplifierchain.

FIG. 7 is a block diagram of an example embodiment of a system 700 inaccordance with the disclosed subject matter. In one embodiment, thesystem 700 may correspond to, for example, the amplifier 210 a and thethreshold adjuster 206 b of FIG. 2; although, it is understood that theabove is merely one illustrative example to which the disclosed subjectmatter is not limited. In one embodiment, the plurality of currentsources 506 may be configured to provide a substantially constant stepsize regardless of temperature, wherein the temperature variation iswithin a predetermined range of operating temperatures (e.g., 0-125 C,etc.).

In various embodiments, such a system or circuit 700 may be used oremployed for intermediate portions of the distributed thresholdadjuster. In various embodiments, a resistive element (e.g., resistiveelements 706 and 706 n) may be used or employed in the amplificationstages that may exhibit variations arising naturally from manufacturingprocesses.

In one embodiment, the plurality of current sources 702 of FIG. 7 usedto bias the gain portion of the individual amplifier stages may becoupled with a proportional to absolute temperature (PTAT) biasingcircuit to reduce the temperature-induced variations in the gain perstage of the multistage amplifier chain. In various embodiments, theconfigurable resistive elements 706 and 706 n may be calibrated using awell-controlled external resistor to reduce the fabrication-inducedvariations arising naturally from semiconductor manufacturing processes.This further reduces variations in the gain per stage of the multistageamplifier chain and advances the goal of an amplifier gain that isconstant within practical limitations. This may differ from someembodiments, in which the input terminal uses or employs un-calibratedresistive elements, as illustrated by FIG. 6.

In various embodiments, each of the plurality of current sources 506 ofFIG. 7 used to bias the threshold adjustment portion (as distinct fromthe gain portion described above) applied at a particular amplifierstage may include a bandgap-based reference current source, particularlywhen the resistive elements 706 and 706 n have been calibrated to reducefabrication-induced variations as described above. In variousembodiments, the bandgap-based reference current source may be generatedvia a bandgap voltage applied to a calibrated resistor biasing element.In such an embodiment, each of the plurality of current sources 506 maybe configured to produce a substantially fixed threshold step sizeregardless of process, supply voltage level and temperature (PVT)variations.

Furthermore, in various embodiments, by switching current either throughthe positive or negative terminals of the current sources 506 the totalcurrent may be kept substantially constant. In such an embodiment, asubstantially fixed common-mode voltage may be maintained. In someembodiments, this may help to maintain substantially constant gainthroughout the multi-stage amplifier.

FIG. 8 is a flow chart of an example embodiment of a technique inaccordance with the disclosed subject matter. In various embodiments,the technique 800 may be used or produced by the systems such as thoseof FIG. 2, 3, 4, 5, 6, or 7. Furthermore, portions of technique 800 maybe used or produced by the systems such as that of FIG. 2, 3, or 4,while another portion of technique 800 may be used or produced by thesystems such as that of FIG. 5, 6, or 7. Although, it is understood thatthe above are merely a few illustrative examples to which the disclosedsubject matter is not limited. Furthermore, it is understood that thedisclosed subject matter is not limited to the ordering of or number ofactions illustrated by technique 800.

Block 802 illustrates that, in one embodiment, an analog input signalmay be received, as described above. In various embodiments, the analoginput signal may include a pair of differential signals, as describedabove. In some embodiments, the analog signal may include an opticalsignal. In yet another embodiment, the analog signal may include signalderived from a wireless electrical signal. In various embodiments, oneor more of the action(s) illustrated by this Block may be performed bythe apparatuses or systems of FIG. 2, 3, 4, 5, 6, or 7, at the inputterminal of FIG. 2, 3, or 4, as described above.

Block 804 illustrates that, in one embodiment, the analog input signalmay be amplified by a predetermined amount of gain, as described above.In one embodiment, this amplification may occur via a multistageamplifier, as described above. In one embodiment, the first portion ofamplifier stages may include non-uniform gain steps, as described above.In various embodiments, one or more of the action(s) illustrated by thisBlock may be performed by the apparatuses or systems of FIG. 2, 3, 4, 5,6, or 7, through the multistage amplifier 210 of FIG. 2, 3, or 4, asdescribed above.

Block 806 illustrates that, in one embodiment, the DC voltage of theanalog input signal may be adjusted, as described above. In oneembodiment, this adjustment may occur via a distributed thresholdadjuster interspersed between the stages of the multistage amplifier, asdescribed above. In various embodiments, the distributed thresholdadjuster may be interspersed between the first portion of amplifierstages, as described above. In one embodiment, the distributed thresholdadjuster may include a plurality of threshold adjusters configured toeach provide a different granularity of DC voltage adjustment to theanalog input signal, as described above. In such an embodiment, each ofthe plurality of threshold adjusters may be configured to be selectivelyturned either on (enabled) or off (disabled), as described above.

In some embodiments, each subsequent threshold adjuster may beconfigured to provide less of a DC voltage adjustment, in terms of thepredetermined amount of gain, than the respective previous thresholdadjuster, as described above. In such an embodiment, while eachthreshold adjuster may provide a substantially equal gain (e.g., 10 mV)in isolation, due to the placement of the individual threshold adjustersamongst the amplifier stages (e.g., providing gains of 1×, 10×, etc.),each of the threshold adjusters may contribute a different level ofadjustment (e.g., 10 mV, 1 mV, etc.) effectively to the input signal, asdescribed above.

In some embodiments, adjusting may include providing a DC voltageadjustment of up to +/−60% of a maximum voltage of the analog inputsignal with an adjustment resolution of less than or equal to 1% of themaximum voltage of the analog input signal, as described above. Invarious embodiments, one or more of the action(s) illustrated by thisBlock may be performed by the apparatuses or systems of FIGS. 2, 3, 4,5, 6, or 7, through the distributed threshold adjuster 206 of FIG. 2, 3,or 4, as described above.

Block 808 illustrates that, in one embodiment, the amount of adjustmentprovided by the distributed threshold adjuster may be controlled basedat least in part upon a measurement of an average DC voltage level ofthe analog input signal eye opening, as described above. In variousembodiments, this control may be provided by including an eye openingmonitor (EOM) configured to measure an average DC voltage level of theanalog input signal eye opening, as described above. In variousembodiments, one or more of the action(s) illustrated by this Block maybe performed by the apparatuses or systems of FIG. 2, 3, 4, 5, 6, or 7,the enable signal(s) 208 of FIG. 2, or the EOM 316 of FIG. 3, asdescribed above.

Block 810 illustrates that, in one embodiment, the amplified analoginput signal may be converted to a digital output signal, as describedabove. In one embodiment, this conversion may include the use oremployment of a slicer or comparator, as described above. In variousembodiments, the output signal may include a pair of differential outputsignals, as described above. In various embodiments, one or more of theaction(s) illustrated by this Block may be performed by the apparatusesor systems of FIG. 2, 3, 4, 5, 6, or 7, through the ADC 212 of FIG. 2,3, or 4 as described above.

FIG. 9 is a flow chart of an example embodiment of a technique inaccordance with the disclosed subject matter. In various embodiments,the technique 900 may be used or produced by the systems such as thoseof FIG. 2, 3, 4, 5, 6, or 7. Furthermore, portions of technique 900 maybe used or produced by the systems such as that of FIG. 2, 3, or 4,while another portion of technique 900 may be used or produced by thesystems such as that of FIG. 5, 6, or 7. Although, it is understood thatthe above are merely a few illustrative examples to which the disclosedsubject matter is not limited. Furthermore, it is understood that thedisclosed subject matter is not limited to the ordering of or number ofactions illustrated by technique 900.

Block 902 illustrates that, in one embodiment, a pair of differentialanalog input signals may be received, as described above. In someembodiments, the analog signals may include optical signals. In yetanother embodiment, the analog signals may include signals derived fromwireless electrical signals. In various embodiments, one or more of theaction(s) illustrated by this Block may be performed by the apparatusesor systems of FIG. 2, 3, 4, 5, 6, or 7, by means of the input terminalof FIG. 5, 6, or 7, as described above.

Block 904 illustrates that, in one embodiment, a plurality of gains maybe applied to the differential analog input signals via a multistageamplifier, as described above. In various embodiments, one or more ofthe action(s) illustrated by this Block may be performed by theapparatuses or systems of FIG. 2, 3, 4, 5, 6, or 7, the multistageamplifier 210 of FIG. 2, 3, or 4, as described above.

Block 906 illustrates that, in one embodiment, a DC voltage of thedifferential input signals may be adjusted by applying an adjustmentcurrent signal to the differential input signals that are the inputs ofthe respective stages of the multistage amplifier, as described above.In various embodiments, this adjustment may occur between at least aportion of stages of the multistage amplifier, as described above.

In various embodiments, adjusting DC voltage of the differential inputsignals may include producing, from a plurality of current sources, anadjustment current whose amperage is dynamically increased or decreasedby fixed steps, as described above. In one embodiment, adjusting DCvoltage of the differential input signals may also include selectivelyturning on or off the plurality of current sources to dynamically selectthe amperage of the adjustment current signal, as described above. Insome embodiments, adjusting DC voltage of the differential input signalsmay also include adding the adjustment current signal to thedifferential input signals, as described above.

In some embodiments, selectively turning on or off the plurality ofcurrent sources to dynamically select the amperage of the adjustmentcurrent signal may include employing a multi-bit digital-to-analogconverter to control whether or not each of the plurality of currentsources is turned on or off, as described above. In such an embodiment,each current source may be controlled by a respective bit of thedigital-to-analog converter, as described above.

In various embodiments, the adjustment current signal may be appliedsuch that a common mode voltage between the differential analog inputsignals remains substantially constant regardless of the amperage of theadjustment current signal, as described above. In various embodiments,one or more of the action(s) illustrated by this Block may be performedby the apparatuses or systems of FIG. 2, 3, 4, 5, 6, or 7, thedistributed threshold adjuster 206 of FIG. 2, 3, or 4, or the currentsources 506 of FIG. 5, 6, or 7 as described above.

Implementations of the various techniques described herein may beimplemented in digital electronic circuitry, or in computer hardware,firmware, software, or in combinations of them. Implementations may beimplemented as a computer program product, i.e., a computer programtangibly embodied in an information carrier, e.g., in a machine-readablestorage device or in a propagated signal, for execution by, or tocontrol the operation of, data processing apparatus, e.g., aprogrammable processor, a computer, or multiple computers. A computerprogram, such as the computer program(s) described above, can be writtenin any form of programming language, including compiled or interpretedlanguages, and can be deployed in any form, including as a stand-aloneprogram or as a module, component, subroutine, or other unit suitablefor use in a computing environment. A computer program can be deployedto be executed on one computer or on multiple computers at one site ordistributed across multiple sites and interconnected by a communicationnetwork.

Method steps may be performed by one or more programmable processorsexecuting a computer program to perform functions by operating on inputdata and generating output. Method steps also may be performed by, andan apparatus may be implemented as, special purpose logic circuitry,e.g., an FPGA (field programmable gate array) or an ASIC (applicationspecific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. Elements of a computer may include atleast one processor for executing instructions and one or more memorydevices for storing instructions and data. Generally, a computer alsomay include, or be operatively coupled to receive data from or transferdata to, or both, one or more mass storage devices for storing data,e.g., magnetic, magneto-optical disks, or optical disks. Informationcarriers suitable for embodying computer program instructions and datainclude all forms of non-volatile memory, including by way of examplesemiconductor memory devices, e.g., EPROM, EEPROM, and flash memorydevices; magnetic disks, e.g., internal hard disks or removable disks;magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor andthe memory may be supplemented by, or incorporated in special purposelogic circuitry.

To provide for interaction with a user, implementations may beimplemented on a computer having a display device, e.g., a cathode raytube (CRT) or liquid crystal display (LCD) monitor, for displayinginformation to the user and a keyboard and a pointing device, e.g., amouse or a trackball, by which the user can provide input to thecomputer. Other kinds of devices can be used to provide for interactionwith a user as well; for example, feedback provided to the user can beany form of sensory feedback, e.g., visual feedback, auditory feedback,or tactile feedback; and input from the user can be received in anyform, including acoustic, speech, or tactile input.

Implementations may be implemented in a computing system that includes aback-end component, e.g., as a data server, or that includes amiddleware component, e.g., an application server, or that includes afront-end component, e.g., a client computer having a graphical userinterface or a Web browser through which a user can interact with animplementation, or any combination of such back-end, middleware, orfront-end components. Components may be interconnected by any form ormedium of digital data communication, e.g., a communication network.Examples of communication networks include a local area network (LAN)and a wide area network (WAN), e.g., the Internet.

While certain features of the described implementations have beenillustrated as described herein, many modifications, substitutions,changes and equivalents will now occur to those skilled in the art. Itis, therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the scope of theembodiments.

What is claimed is:
 1. A distributed threshold adjuster (DTA)interspersed between a plurality of stages of a multistage amplifier andconfigured to adjust the DC voltage of an input signal to facilitate adecision by an analog-to-digital converter (ADC) comprising: an inputsignal terminal configured to receive the input signal; a plurality ofcurrent sources configured to produce an adjustment current signal whoseamperage is configured to be increased or decreased by fixed steps inorder to adjust the DC voltage of the input signal, wherein each of theplurality of current sources are configured to provide a current thatmay be selectively added or subtracted from the input signal; a controlunit configured to selectively turn on or off the individual currentsources of the plurality of current sources to select the amperage ofthe adjustment current signal; and an output terminal configured toproduce an output signal, comprising a combination of the input signaland the adjustment current signal, to a stage of a multistage amplifier.2. The DTA of claim 1, wherein the output terminal is coupled with theinput terminal and the current sources.
 3. The DTA of claim 1, whereinthe input signal terminal includes a coupling capacitor configured topass the AC portion of the input signal to the output terminal.
 4. TheDTA of claim 1, wherein the input signal includes a pair of differentialinput signals, and the output signal includes a pair of differentialoutput signals; and the DTA further includes a pair of resistors coupledin series with respect to one another and in parallel with respect tothe output terminal, and configured such that a common mode voltage(Vcm) exists between the pair of resistors.
 5. The DTA of claim 4,wherein the plurality of current sources are coupled between the inputterminal and the pair of resistors; and the plurality of current sourcesare coupled such that the output common mode voltage remainssubstantially constant regardless of the amperage of the adjustmentcurrent source.
 6. The DTA of claim 4, wherein the plurality of currentsources are configured to produce a positive adjustment current signaland a negative adjustment current signal; wherein the input signalincludes a differential analog input signal; and wherein the positiveadjustment signal and the negative adjustment signal are interchangeablyapplied to the differential analog input signal.
 7. The DTA of claim 1,wherein the plurality of current sources are configured to provide asubstantially constant step size regardless of temperature.
 8. The DTAof claim 7, wherein the plurality of current sources may be configuredto produce a substantially fixed threshold step size regardless ofprocess, supply voltage level and temperature variations.
 9. A systemcomprising: a receiver configured to receive a pair of differentialanalog input signals; a multistage amplifier configured to amplify theanalog input signals by an amount of gain; a plurality of distributedthreshold adjusters (DTAs) interspersed between the stages of themultistage amplifier, and configured to adjust the DC voltages of thedifferential analog input signals to facilitate a decision by ananalog-to-digital converter (ADC), and wherein each of the distributedthreshold adjusters includes: a plurality of current sources configuredto produce an adjustment current signal whose amperage is configured tobe increased or decreased by fixed steps in order to adjust the DCvoltage of the input signal, and a control unit configured toselectively turn on or off the individual current sources of theplurality of current sources to select the amperage of the adjustmentcurrent signal; and the ADC configured to convert the amplified analoginput signals to a digital output signal.
 10. The system of claim 9,wherein each of the DTAs further includes a pair of resistors coupled inseries with respect to one another and in parallel with respect to theoutput terminals of the DTA, and configured such that a common modevoltage (Vcm) exists between the pair of resistors.
 11. The system ofclaim 10, wherein the plurality of current sources are coupled betweenthe input terminals of the respective DTA and the pair of resistors; andthe plurality of current sources are coupled such that the common modevoltage remains substantially constant regardless of the amperage of theadjustment current source.
 12. The system of claim 9, wherein theplurality of current sources are configured to produce a positiveadjustment current signal and a negative adjustment current signal;wherein the input signal includes a differential analog input signal;and wherein the positive adjustment signal and the negative adjustmentsignal are interchangeably applied to the differential analog inputsignal.
 13. The system of claim 12, wherein the absolute values of theamperage of the positive and negative adjustment current signals aresubstantially equal to maintain a relatively constant output common-modevoltage per amplifier stage and minimizing an operating-point inducedgain variation per amplifier stage.
 14. The system of claim 9, whereinthe plurality of current sources are configured to provide asubstantially constant step size regardless of temperature.
 15. Thesystem of claim 14, wherein the plurality of gain stages comprising themultistage amplifier chain are coupled with a proportional to absolutetemperature (PTAT) biasing circuit to reduce temperature-inducedvariations in the gain per amplifier stage.
 16. The system of claim 14,wherein the plurality of current sources employed to provide thethreshold adjustment are coupled with either a calibrated or anuncalibrated bandgap biased resistor, depending on whether thecorresponding load resistor through which the applied current flows iscalibrated or uncalibrated, to provide a substantially constant stepsize regardless of temperature, supply-voltage changes orfabrication-induced variations.
 17. The system of claim 14, wherein eachof the plurality of current sources employed to provide the thresholdadjustment includes a bandgap-based reference current source.
 18. Amethod comprising: receiving a pair of differential analog inputsignals; applying a plurality of gains to the differential analog inputsignals via a multistage amplifier; and in between at least a portion ofstages of the multistage amplifier, adjusting a DC voltage of thedifferential input signals by applying an adjustment current signal tothe differential input signals that are the inputs of the respectivestages of the multistage amplifier.
 19. The method of claim 18, whereinapplying an adjustment current signal comprises: producing, from aplurality of current sources, an adjustment current signal whoseamperage is dynamically increased or decreased by fixed steps,selectively turning on or off the plurality of current sources todynamically select the amperage of the adjustment current signal, andadding the adjustment current signal to the differential input signals.20. The method of claim 19, wherein selectively turning on or off theplurality of current sources to dynamically select the amperage of theadjustment current signal includes: employing a multi-bitdigital-to-analog converter to control whether or not each of theplurality of current sources is turned on or off; and wherein eachcurrent source is controlled by a respective bit of thedigital-to-analog converter.